The present invention relates generally to shunt feedback amplifiers, and in particular to an improved bootstrapped shunt feedback amplifier.
U.S. Pat. No. 3,868,580 describes a bootstrapped shunt feedback amplifier having the capability of providing large, fast voltage changes efficiently and accurately while driving capacitive loads. The amplifier is designed so that an input signal drives a common-emitter transistor stage, and the output is connected between the collector of the common-emitter stage and a bootstrapped emitter follower output stage. This arrangement permits the amplifier to supply large load currents of either polarity, and a current-steering circuit permits the output voltage to slew through its dynamic range without any dead zones due to transistors switching on and off, so as to preclude distortion of the output waveform. To accomodate large voltage swings, this prior art amplifier was expanded by stacking additional transistors in totem-pole fashion both for the shunt feedback amplifier lower portion and for the emitter follower upper portion thereby to eliminate high-voltage stress on any of the active devices within the amplifier. A decided disadvantage in this amplifier design is that many transistors are required to effect proper operation without stressing the shunt feedback amplifier transistors, and, moreover, as transistors are added, precise control over the output voltage is somewhat diminished. Particularly in oscilloscopes, a precise replication of signals over large voltage swings is required to accurately drive the deflection plates.